The invention relates to a projector for projecting fixed stars, preferably for use in planetaria.
In all existing planetaria, the brightness of the starry sky shown is a crucial and central problem. To achieve a natural impression of the sky, it is necessary to portray very small disks as brightly as possible at the dome. The full sphere of the projector must be illuminated with this projection, although the ratio of the area of the actually bright regions to the area of the full sphere is about 1 to 10.sup.5.
From the book by Letsch, "Das Zeiss-Planetarium" (The Zeiss Planetarium), Gustav Fischer Verlag, Jena, 1955, the reprint "Bild der Wissenschaft" (Picture of Science), Deutsche Verlagsgesellschaft Stuttgart, 1977, and "Jenaer Rundschau" (1967), 3, pages 177 to 181 and (1968), 6, pages 345 to 349, those involved with the construction of planetaria know that, for the projection of fixed stars, projectors may be provided on hollow spheres.
A light source, disposed centrally in each hollow sphere, supplies all projectors with light. Each projector is provided with a transparency, the pictorial content of which comprises small, transparent areas in absorbing material corresponding to the stars of the star field in question, which are to be projected. These transparencies generally are each illuminated from a central light source through respective condensers each associated with a respective one of the transparencies and the light passing through each transparency is projected by a respective lens on to the inside of the dome.
Generally, all projections, in which, because of the pictorial content of the transparency, only a small proportion of the light is used for the imaging, as is the case with most of the projected objects in planetaria, have the disadvantage that the bulk of the light, produced by the light source, is finally converted into unwanted heat. To improve the brilliance and brightness of the images of the stars, it was necessary to increase the output of the light source, which, on the other hand, increased the amount of heat developed.
Individual projection systems, some with their own light sources, are also used in various planetaria to portray the brightest stars. The attempt has also been made to project a computer-generated image of the sky of a cathode ray tube through over a fish eye optical system on to the dome. The sky, so projected, is however of very low luminosity.
With the help of the resonator construction which is described in the DD Pat. No. 153,933 and in which the light that is not used for the projection is always returned again to the lens (transparency) by multiple reflections, the utilization of the light is admittedly already clearly better than that achieved with the above-described devices, but does not reach the theoretically possible maximum level and essentially assumes the use of small light sources of high light density. The manufacture of the resonators is technologically very sophisticated and these resonators require relatively much space within the projectors.
From the DD Pat. No. 154,921, a device for projecting stars is known in which several projectors are provided on a sphere or a polyhedron in mountings about a centrally disposed light source. To reduce light losses, the projectors are disposed as close to one another as possible. With this device also, only a small portion of the light emanating from the light source is utilized for the actual projection of the stars.
It is the object of the invention to eliminate the disadvantages of the state of the art and to increase the light utilization for projections in planetaria.
The invention is based on the task of providing a projector for projecting fixed stars, with which an increase in brightness, an increase in the brilliance of the image and a decrease in the amount of heat transferred to the instrument is achieved by using fiber optical light guides in fixed star projectors.